Rackspace Orchestration has the ability to modify running stacks using
the update stack operation.
This gives you the ability to add, edit, or delete resources in a
stack. In the python-heatclient CLI, this operation is called heatstack-update.

Modifying some resource properties will trigger a delete->rebuild of
that resource. Because some architectures are less tolerant of nodes
being rebuilt, you can check the Template Guide
to see which properties trigger a rebuild. For example, each property
in the OS::Nova::Server documentation
says either "Updates cause replacement" or "Can be updated without
replacement".

Alternatively, you can preview what will happen with the stack is
updated by adding a "-y" option to the "heat stack-update" command:

heatstack-update-y-fstack-update-example.yamlstack-update-example

The hello_world resource should show up in the "updated" section,
since resizing can be done without replacement.

To actually update the stack, resubmit the modified template:

heatstack-update-fstack-update-example.yamlstack-update-example

If there were any parameters or flags passed to the original
stack-create, they need to be passed unmodified to the stack-update
command (unless you are changing them as part of the stack-update).
Leaving them out may result in unexpected changes to the stack.